Fe-si-b-cu-nb-m (m = Al, Ni) Fe-based Amorphous And Nanocrystalline Alloy Soft Magnetic Properties

Fe-based amorphous alloys and nanocrystalline alloys (e.g., the FINEMET alloy), which are obtained by crystallization of the amorphous precursors, have very excellent soft magnetic properties. Because of the outstanding, combined soft magnetic properties, the engineering application of the FINEMET-type nanocrystalline materials is quite promising. In this thesis, a series of FINEMET-type alloys are obtained by partial substititution of Al or Ni for Nb. The soft magnetic properties, crystallization kinetics of Fe-Si-B-Cu-Nb-M (M=Al, Ni) amorphous alloys are investigated.The alloy ingots were prepared by arc melting under the titanium-gettered argon atomsphere. A single-roller melt spinning method was employed to prepare Fe_73.5Si_13.5B9_Cu₁Nb_3-xM_x (x=0, 0.5, 0.8, 1.0, 1.5) amorphous ribbons. The microstructure and magnetic properties of the amorphous and annealed alloys ribbons were investigated by X-ray diffractometer (XRD), differential scanning calorimetry (DSC), vibrating sample magnetometer (VSM) and B-H analyzer. The diameters of nano-grains are estimated by Schller formula, from which the influences of Al or Ni for amorphous crystallization behaviors are discussed. With the addition of Al or Ni to the Fe-Si-B-Cu-Nb alloy, the average diameter of the nano-grains increases slightly. The magnetic properties of the as-cast ribbons were measured by VSM. The results show that the saturation induction densities (Bs) of the ribbons first decrease and then increase with increasing Al or Ni contents. On the other hand, the addition of Al enhances the soft magnetic properties by decreasing coercivity, while Ni increases the saturation induction density. The combined soft magnetic properties are obtained in the Fe_73.5Si_13.5B₉Cu₁Nb₂Al₁ amorphous alloy.The influences of the partial substitution of Ni or Al for Nb on the soft magnetic properties of the nanocrystalline Fe_73.5Si_13.5B₉Cu₁Nb₃(FINEMET)alloy are investigated. The nanocrystalline alloys are obtained by annealing of the amorphous precursors at different annealing temperatures. The results indicate that the partial substitution of Ni or Al for Nb results in the increase of saturation magnetic induction density (Bs). Good soft magnetic properties are obtained as the contents of Al or Ni reach 1.0 at. %. Higher Bs is obtained for the alloys with Ni element. However, the addition of Al is favorable for the decrease of coercive force (Hc).The influences of Al and Ni on the magnetic properties are also discussed. After annealing, the nanocrystalline grains of Fe-Si-B-Cu-Nb-Ni and Fe-Si-B-Cu-Nb-Al alloys areα-FeNi(Si) andα-FeAl(Si) respectively. The magneto-crystalline anisotropy constant (K1) ofα-FeNi(Si) is larger than that ofα-FeAl(Si). So the Hc of the Fe-Si-B-Cu-Nb-Ni alloy is higher than that of Fe-Si-B-Cu-Nb-Al alloy alloy. Ni is a ferromagnetism element, resulting in a higher Bs of the Fe-Si-B-Cu-Nb-Ni alloy.